Microelectrochemical Testing of Cerium-Based Conversion Coatings
The corrosion resistance of cerium-based conversion coatings was evaluated using a ~50 μm diameter capillary probe. The tests showed three distinct regions during electrochemical impedance spectroscopy and potentiodynamic testing: active, intermediate, and passive. Active regions had total impedance values of less than 200 Ω·cm2 and corrosion current densities (icorr) greater than 1x10-4 Amps/cm 2. Passive regions had total impedance values greater than 10 KΩ·cm2 and icorr values less than 1x10-5 Amps/cm2. The total impedance and icorr values for intermediate regions were between those for active and passive regions. Both active and intermediate regions displayed mixed open circuit potentials ranging from -0.50 V to -0.85 V vs. SCE, which showed that the coatings were susceptible to galvanic corrosion. The ability to isolate and probe specific surface features can provide insight into the corrosion mechanism as well as where corrosion is likely to initiate.
S. G. Joshi et al., "Microelectrochemical Testing of Cerium-Based Conversion Coatings," ECS Transactions, vol. 25, no. 29, pp. 19-30, Electrochemical Society, Inc., Jan 2010.
The definitive version is available at http://dx.doi.org/10.1149/1.3327221
Coatings for Corrosion Protection - 216th ECS Meeting (2009: Oct. 4-9, Vienna, Austria)
Materials Science and Engineering
Keywords and Phrases
Active regions; Conversion coatings; Corrosion current densities; Corrosion mechanisms; Galvanic corrosion; Open circuit potential; Potentiodynamic testing; Specific surface
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Article - Conference proceedings
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